linuxsessionmgr: make browser detection more robust

In non-WSL environments we make our checks for a browser more
robust by checking for a 'shell execute' handler (like xdg-open).
Previously we just relied on a desktop session ($DISPLAY or
$WAYLAND_DISPLAY), which isn't accurate since in `OpenBrowser`
we require a shell execute handler. The check and implementation
are now aligned!

We refactor the method to avoid nesting `if`s and use early returns to
make things a little clearer.

Helped-by: Marc Becker <becm@gmx.de>
Co-authored-by: Kyle Rader <kyrader@microsoft.com>
Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>

Author: mjcheetham

src/shared/Core/Interop/Linux/LinuxSessionManager.cs

@@ -53,45 +53,42 @@ protected override void OpenBrowserInternal(string url)
 
     private bool GetWebBrowserAvailable()
     {
-        // If this is a Windows Subsystem for Linux distribution we may
-        // be able to launch the web browser of the host Windows OS.
-        if (WslUtils.IsWslDistribution(Environment, FileSystem, out _))
+        // We need a shell execute handler to be able to launch to browser
+        if (!TryGetShellExecuteHandler(Environment, out _))
         {
-            // We need a shell execute handler to be able to launch to browser
-            if (!TryGetShellExecuteHandler(Environment, out _))
-            {
-                return false;
-            }
-
-            //
-            // If we are in Windows logon session 0 then the user can never interact,
-            // even in the WinSta0 window station. This is typical when SSH-ing into a
-            // Windows 10+ machine using the default OpenSSH Server configuration,
-            // which runs in the 'services' session 0.
-            //
-            // If we're in any other session, and in the WinSta0 window station then
-            // the user can possibly interact. However, since it's hard to determine
-            // the window station from PowerShell cmdlets (we'd need to write P/Invoke
-            // code and that's just messy and too many levels of indirection quite
-            // frankly!) we just assume any non session 0 is interactive.
-            //
-            // This assumption doesn't hold true if the user has changed the user that
-            // the OpenSSH Server service runs as (not a built-in NT service) *AND*
-            // they've SSH-ed into the Windows host (and then started a WSL shell).
-            // This feels like a very small subset of users...
-            //
-            if (WslUtils.GetWindowsSessionId(FileSystem) == 0)
-            {
-                return false;
-            }
+            return false;
+        }
 
-            // If we are not in session 0, or we cannot get the Windows session ID,
-            // assume that we *CAN* launch the browser so that users are never blocked.
-            return true;
+        // If this is a Windows Subsystem for Linux distribution we may
+        // be able to launch the web browser of the host Windows OS, but
+        // there are further checks to do on the Windows host's session.
+        //
+        // If we are in Windows logon session 0 then the user can never interact,
+        // even in the WinSta0 window station. This is typical when SSH-ing into a
+        // Windows 10+ machine using the default OpenSSH Server configuration,
+        // which runs in the 'services' session 0.
+        //
+        // If we're in any other session, and in the WinSta0 window station then
+        // the user can possibly interact. However, since it's hard to determine
+        // the window station from PowerShell cmdlets (we'd need to write P/Invoke
+        // code and that's just messy and too many levels of indirection quite
+        // frankly!) we just assume any non session 0 is interactive.
+        //
+        // This assumption doesn't hold true if the user has changed the user that
+        // the OpenSSH Server service runs as (not a built-in NT service) *AND*
+        // they've SSH-ed into the Windows host (and then started a WSL shell).
+        // This feels like a very small subset of users...
+        //
+        if (WslUtils.IsWslDistribution(Environment, FileSystem, out _) &&
+            WslUtils.GetWindowsSessionId(FileSystem) == 0)
+        {
+            return false;
         }
 
-        // We require an interactive desktop session to be able to launch a browser
-        return IsDesktopSession;
+        // If we are not in WSL, or we are but are not in session 0 (or we cannot get
+        // the Windows session ID), assume that we *CAN* launch the browser so that
+        // users are never blocked.
+        return true;
     }
 
     private static bool TryGetShellExecuteHandler(IEnvironment env, out string shellExecPath)